1. Field of the Invention
The invention relates to golf balls with cores or intermediate layers prepared from melt-processible thermoplastic compositions comprising organic acids or salts of organic acids and neutralized copolymers of ethylene and C3 to C8 α,β ethylenically unsaturated carboxylic acids.
2. Description of Related Art
Several patents and publications are cited in this description in order to more fully describe the state of the art to which this invention pertains. The entire disclosure of each of these patents and publications is incorporated by reference herein.
Premium golf balls include wound balls, two-piece balls and multilayered balls. Wound balls may have a spherical molded center, elastomeric thread-like material wound around the center, and either a thermoplastic or thermoset cover. Two-piece balls have a spherical molded core covered with a thin layer of thermoplastic or thermoset material. Multilayered balls have a spherical molded core, a cover, and one or more intermediate layers between the core and the cover.
Centers for wound balls and cores for two-piece and multi-layer balls have been made using a thermoset rubber such as polybutadiene rubber. With thermoset rubber, complex multi-step processes are needed to make cores and centers. These processes result in scrap that is difficult to recycle. Attempts to solve these difficulties by substituting a thermoplastic for the thermoset rubber have had limited success. Thermoplastic ionomers of copolymers of alpha olefins, particularly ethylene, and C3-8 α,β ethylenically unsaturated carboxylic acids have found utility in golf ball components such as covers, and other applications. U.S. Pat. No. 3,264,272 teaches methods for making such ionomers. The acid copolymers on which the ionomers are based may be prepared as described in U.S. Pat. No. 4,351,931.
Some ionomer compositions, and golf ball covers comprising these compositions, are described in U.S. Pat. Nos. 5,688,869; 6,150,470; 6,277,921; 6,433,094; 6,451,923; 6,573,335 and 6,800,695. The ionomer compositions comprise metal cation neutralized high acid ionomer resins comprising copolymers of greater than 16% by weight of an alpha,beta-unsaturated carboxylic acid and the balance an alpha-olefin, of which about 10 to about 90% of the acid groups of the copolymer are neutralized with metal cations.
Ionomers have also been modified with fatty acids. For example, U.S. Pat. No. 6,777,472 describes a thermoplastic composition that is melt-processible consisting essentially of (a) from 20 to 45 weight % aliphatic, mono-functional organic acid(s) having fewer than 36 carbon atoms or salt(s) thereof; and (b) ethylene, C3 to C8 alpha,beta ethylenically unsaturated carboxylic acid copolymer(s) or melt-processible ionomer(s) thereof, wherein greater than 90% of all the acid of (a) and (b) is neutralized by concurrently or subsequently adding to the melt blend of (a) and (b) an amount of a cation source necessary to obtain greater than 90% neutralization.
Modified ionomers have been used as golf ball components. U.S. Pat. No. 6,565,456 describes multilayer golf balls comprising a solid core, a surrounding layer, an intermediate layer and a cover, wherein at least one of the surrounding layer, the intermediate layer or the cover is formed of a heated mixture comprising (a) an olefin-carboxylic acid-optional carboxylate random copolymer and/or (d) a metal ion-neutralized olefin-carboxylic acid-optional carboxylate random copolymer; (b) a fatty acid or derivative; and (c) a neutralizing basic inorganic metal compound.
It is desirable to provide a high performance material to be used in the cores, centers or intermediate layers of golf balls.